The head of the U.N.'s nuclear watchdog said Monday the agency needs more transparency from Syria and other nations to determine whether traces of uranium found at a site bombed by Israeli planes indicate Damascus was building a nuclear reactor there.

International Atomic Energy Agency chief Mohamed ElBaradei confirmed that the radioactive material was found at the site, but said the source was inconclusive.

"It's not highly enriched uranium. It could have come from so many different ways," he told reporters in Dubai. "That's why we're looking at so many different scenarios."

Uranium can be found naturally in low concentrations and must be "enriched" before it can be used in either power plants or nuclear weapons. Highly enriched uranium is the type used in atomic bombs.

ElBaradei made the comments during and after a speech to business leaders here, just days before the IAEA is expected to circulate a confidential report to board members outlining the status of his agency's investigation.

"We still have a lot of work to do. We haven't yet reached a conclusion whether that was a reactor or not a reactor," ElBaradei said.

Diplomats told the AP earlier this month that soil samples collected at the bombed site revealed minute traces of processed uranium.

Syria's foreign minister, Walid al-Moallem, last week that the leaks to the media about the uranium were meant to put pressure on the country, which has denied any wrongdoing.

The IAEA chief called specifically for more cooperation from Damascus, saying it needs "a lot of transparency on the part of Syria." He said he was hopeful that Syria would allow inspectors back into the country to carry out further tests.

But he also said Israel needs to provide more information to address Syrian allegations that the uranium may have come from Israeli bombs dropped on the site during the September 2007 raid.

Al-Moallem last week said it was unclear what type of bombs targeted the site, adding that the United States has used bombs containing depleted uranium in Iraq and Afghanistan. The Israeli Foreign Ministry had no comment on the matter when asked last week.

ElBaradei also called on countries that have satellite images of the site to cooperate with the investigation.

"We need cooperation from everybody," he said. "We are not going to be able to reach a quick conclusion or jump the gun unless we have absolutely credible information."